MXenes are a new type of two-dimensional carbides with rich physical and chemical properties. The physics of MXenes, and thus the applications, are dominated by surface functional groups. Herein, the effects of differ...MXenes are a new type of two-dimensional carbides with rich physical and chemical properties. The physics of MXenes, and thus the applications, are dominated by surface functional groups. Herein, the effects of different terminations(O,S, Se, Te) on the geometric and electronic properties of Nb_(2)C MXenes were studied via density functional theory(DFT)calculations. Three adsorption sites were examined to determine the most stable configurations. The results showed that both the types and the positions of surface functional groups influence the geometric stability and physical characters of Nb_(2)C. The S and Se terminations make the Nb_(2)C MXenes to be semiconductor, while Nb_(2)C MXenes with other terminations(O, Te) are conductor. The electron location function, density of states, Bader charge distribution, and the projected crystal orbital Hamilton population were conducted to explain the origin of adsorption stability and electronic nature difference. Our results provide a fundamental understanding about the effects of surface terminations on the intrinsic stability and electronic properties of Nb_(2)C MXenes.展开更多
Quaternary carbide Ti3NiAl2C ceramics has been investigated as a potential nuclear fusion structural material,and it has advantages in certain aspects compared with Ti2AlC,Ti3AlC2,and Ti3SiC2 structural materials.In t...Quaternary carbide Ti3NiAl2C ceramics has been investigated as a potential nuclear fusion structural material,and it has advantages in certain aspects compared with Ti2AlC,Ti3AlC2,and Ti3SiC2 structural materials.In this paper,quaternary carbide Ti3NiAl2C ceramics is pressurized to investigate its structural,mechanical,electronic properties,and Debye temperature.Quaternary carbide Ti3NiAl2C ceramics still maintains a cubic structure under pressure(0–110 GPa).At zero pressure,quaternary carbide Ti3NiAl2C ceramics only has three bonds:Ti–Al,Ni–Al,and Ti–C.However,at pressures of 20 GPa,30 GPa,40 GPa,60 GPa,and 70 GPa,new Ti–Ni,Ti–Ti,Al–Al,Ti–Al,and Ti–Ti bonds form.When the pressure reaches 20 GPa,the covalent bonds change to metallic bonds.The volume of quaternary carbide Ti3NiAl2C ceramics can be compressed to 72%of its original volume at most.Pressurization can improve the mechanical strength and ductility of quaternary carbide Ti3NiAl2C ceramics.At 50–60 GPa,its mechanical strength can be comparable to pure tungsten,and the material changes from brittleness to ductility.However,the degree of anisotropy of quaternary carbide Ti3NiAl2C ceramics increases with the increasing pressure.In addition,we also investigated the Debye temperature,density,melting point,hardness,and wear resistance of quaternary carbide Ti3NiAl2C ceramics under pressure.展开更多
With OLYMPUS PMG3 metallograph, an abnormal three-layer gradient structure, i. e. coarse grain zone, binder enrichment zone and normal structure zone from surface to inner, was observed in Cr3C2 based cemented carbide...With OLYMPUS PMG3 metallograph, an abnormal three-layer gradient structure, i. e. coarse grain zone, binder enrichment zone and normal structure zone from surface to inner, was observed in Cr3C2 based cemented carbide. In the binder enrichment zone, three different shapes of anomalous coarse carbides were observed. It is shown that the transverse rupture strength can be raised remarkably, up 20.7%from the alloy with abnormal gradient structure by removing the abnormal gradient structure. The results suggested that the abnormal gradient structure in the surface, especially the anomalous coarse carbides in the binder enrichment zone is the main reason for the lower strength展开更多
Mo2C was prepared by microwave plasma chemical vapor deposition(MPCVD)technique with the power of 800 W and pressure of 18 kPa.Compared with traditional preparation methods,MPCVD has faster growth rate and higher puri...Mo2C was prepared by microwave plasma chemical vapor deposition(MPCVD)technique with the power of 800 W and pressure of 18 kPa.Compared with traditional preparation methods,MPCVD has faster growth rate and higher purity of the products.The influence of growth time on the morphology and structure of Mo_(2)C was characterized by X-ray diffraction and Scanning Electron Microscopy.The photocatalytic performance of Mo_(2)C was tested.It was found that Mo_(2)C had good photocatalytic performance and the 6 h sample had the highest photodegradation rate,indicating the great potential of Mo_(2)C as photocatalyst.展开更多
The morphology,microstructure and decomposition behavior of M2C carbides in high speed steels with different chemical compositions have been investigated by scanning electron microscopy,transmission electron microscop...The morphology,microstructure and decomposition behavior of M2C carbides in high speed steels with different chemical compositions have been investigated by scanning electron microscopy,transmission electron microscopy,electron backscatter diffraction and X-ray diffraction.The results show that the morphology and substructure of M2C carbides are very sensitive to chemical compositions of high speed steels.M2C carbides present the plate-like shape in tungsten-molybdenum steel and present the polycrystal orientation in the eutectic cell.In contrast,they show the fibrous shape in molybdenum-base steel and exhibit the monocrystal orientation.Plate-like and fibrous M2C carbides are both metastable and decompose into M6 C together with MC at high temperatures.MC nucleates inside the plate-like M2C while it is formed at the fibrous M2C/matrix interface during the decomposition process.Such differences are expected to arise from different compositions of plate-like and fibrous M2C carbides.展开更多
Novel two-dimensional(2D)Nb_(2)C nanosheets were successfully prepared through a simple lultrasonic and magnetic stirring treatment from the original accordion-like powder.To further study their water-lubrication prop...Novel two-dimensional(2D)Nb_(2)C nanosheets were successfully prepared through a simple lultrasonic and magnetic stirring treatment from the original accordion-like powder.To further study their water-lubrication properties and deal with common oxidation problems,Nb_(2)C nanosheets with different oxidation degrees were prepared and achieved long-term stability in deionized water.Scanning electron microscope(SEM),transmission electron microscope(TEM),scanning probe microscope(SPM),X-ray powder diffraction(XRD),Raman,and X-ray photoelectron spectrometer(XPS)experiments were utilized to characterize the structure,morphology,and dispersion of Nb_(2)C nanosheets with different degrees of oxidation.The tribological behaviors of Nb_(2)C with different degrees of oxidation as additives for water lubrication were characterized using a UMT-3 friction testing machine.The wear scars formed on the 316 steel surface were measured using three-dimensional(3D)laser scanning confocal microscopy.The tribological results showed that a moderately oxidized Nb_(2)C nanosheet,which owned the composition of Nb_(2)C/Nb_(2)O5/C,displayed excellent tribological performance,with the friction coefficient(COF)decreasing by 90.3%and a decrease in the wear rate by 73.1%compared with pure water.Combining the TEM and Raman spectra,it was shown that Nb_(2)O5 nanoparticles filled in the worn zone,and the layered Nb_(2)C and C were adsorbed into the surface of the friction pair to form a protective lubricating film.This combined action resulted in an excellent lubricating performance.展开更多
Nb_(2)S_(2)C is a van der Waals type layered superconductor with a transition temperature Tc=7.6 K.In this paper,detailed calculations of the electronic structure and topological properties of Nb_(2)S_(2)C were perfor...Nb_(2)S_(2)C is a van der Waals type layered superconductor with a transition temperature Tc=7.6 K.In this paper,detailed calculations of the electronic structure and topological properties of Nb_(2)S_(2)C were performed from first principles.We find that Nb2S2C is a highly anisotropic metal with multi-band characteristics.In the absence of spin-orbit coupling(SOC),there appears one pair of triply degenerate points created by band inversion along the Γ-A line.When SOC is considered,the triple points are gapped.Intriguingly,two distinct types of topological states,including topological Dirac semimetal and topological insulator states,co-emergence in the vicinity of Fermi level.Moreover,the topology of Nb_(2)S_(2)C is robust to external pressure and the Fermi level can be shifted downward to the topological Dirac semimetal state and topological insulator state at 10 GPa and 14 GPa,respectively.The results herein provide a new platform not only for the studies of physics of low-dimensional superconductor but also for further investigations of topological superconductivity.展开更多
Extensive research has been devoted to lithium-sulfur(Li-S)batteries due to their overwhelming promises and advantages such as high theoretical capacity(1675 m Ah g^(-1)),extremely cost effectiveness and abundance and...Extensive research has been devoted to lithium-sulfur(Li-S)batteries due to their overwhelming promises and advantages such as high theoretical capacity(1675 m Ah g^(-1)),extremely cost effectiveness and abundance and availability of sulfur.Nevertheless,a sluggish electrochemical kinetics of the battery limited by a slow conversion of lithium polysulfide(LiPSs)intermediates and Li PSs shuttle effect severely hinder its development towards industrial application.Herein,we designed the oxidized Nb2_(C)MXene with amorphous carbon(Nb_(2)O_(5)/C)composites as sulfur host using CO_(2)treatment to address the above issues.The Nb_(2)O_(5)/C composites with high conductivity are directly employed as sulfur hosts for Li-S battery capable to remarkably mitigate the shuttle phenomenon due to a combined effect of their Li PSs trapping ability and catalytic activity towards their accelerated conversion.Meanwhile,the unique layered structure of the composite facilitates ion transfer and accommodates the volume changes of the cathode during cycling.With this rational design,the resultant Li-S batteries exhibit superior electrochemical performance with a high initial specific capacity of 745 m Ah g^(-1)at 1.0 C and a reversible capacity of 620 m Ah g^(-1)at a high rate cycling at 3.0 C.展开更多
基金National Natural Science Foundation of China(Nos.82171030,81870678)Natural Science Foundation of Hunan Province,China(No.2021JJ30925)+1 种基金Health Commission of Hunan Province,China(No.B202307026146)Natural Science Foundation of Hainan Province,China(No.821QN1005)。
基金Project supported by the National Natural Science Foundation of China (Grant Nos. U1804130, U2004212, 11904084, and 11874141)the Henan Overseas Expertise Introduction Center for Discipline Innovation (Grant No. CXJD2019005)+1 种基金the China Postdoctoral Science Foundation (Grant No. 2021M690933)the Key Scientific Research Projects of Henan Education Department, China (Grant No. 22A140020)。
文摘MXenes are a new type of two-dimensional carbides with rich physical and chemical properties. The physics of MXenes, and thus the applications, are dominated by surface functional groups. Herein, the effects of different terminations(O,S, Se, Te) on the geometric and electronic properties of Nb_(2)C MXenes were studied via density functional theory(DFT)calculations. Three adsorption sites were examined to determine the most stable configurations. The results showed that both the types and the positions of surface functional groups influence the geometric stability and physical characters of Nb_(2)C. The S and Se terminations make the Nb_(2)C MXenes to be semiconductor, while Nb_(2)C MXenes with other terminations(O, Te) are conductor. The electron location function, density of states, Bader charge distribution, and the projected crystal orbital Hamilton population were conducted to explain the origin of adsorption stability and electronic nature difference. Our results provide a fundamental understanding about the effects of surface terminations on the intrinsic stability and electronic properties of Nb_(2)C MXenes.
基金Project supported by Fujian Science&Technology Innovation Laboratory for Energy Devices of China(21C-LAB)(Grant No.21C-OP-202013)the National Natural Science Foundation of China(Grant No.12064027)+1 种基金the International Science and Technology Cooperation Program of China(Grant No.2015DFA61800)the Scientific Research Fund of Jiangxi Provincial Education Department,China(Grant No.GJJ180973).
文摘Quaternary carbide Ti3NiAl2C ceramics has been investigated as a potential nuclear fusion structural material,and it has advantages in certain aspects compared with Ti2AlC,Ti3AlC2,and Ti3SiC2 structural materials.In this paper,quaternary carbide Ti3NiAl2C ceramics is pressurized to investigate its structural,mechanical,electronic properties,and Debye temperature.Quaternary carbide Ti3NiAl2C ceramics still maintains a cubic structure under pressure(0–110 GPa).At zero pressure,quaternary carbide Ti3NiAl2C ceramics only has three bonds:Ti–Al,Ni–Al,and Ti–C.However,at pressures of 20 GPa,30 GPa,40 GPa,60 GPa,and 70 GPa,new Ti–Ni,Ti–Ti,Al–Al,Ti–Al,and Ti–Ti bonds form.When the pressure reaches 20 GPa,the covalent bonds change to metallic bonds.The volume of quaternary carbide Ti3NiAl2C ceramics can be compressed to 72%of its original volume at most.Pressurization can improve the mechanical strength and ductility of quaternary carbide Ti3NiAl2C ceramics.At 50–60 GPa,its mechanical strength can be comparable to pure tungsten,and the material changes from brittleness to ductility.However,the degree of anisotropy of quaternary carbide Ti3NiAl2C ceramics increases with the increasing pressure.In addition,we also investigated the Debye temperature,density,melting point,hardness,and wear resistance of quaternary carbide Ti3NiAl2C ceramics under pressure.
文摘With OLYMPUS PMG3 metallograph, an abnormal three-layer gradient structure, i. e. coarse grain zone, binder enrichment zone and normal structure zone from surface to inner, was observed in Cr3C2 based cemented carbide. In the binder enrichment zone, three different shapes of anomalous coarse carbides were observed. It is shown that the transverse rupture strength can be raised remarkably, up 20.7%from the alloy with abnormal gradient structure by removing the abnormal gradient structure. The results suggested that the abnormal gradient structure in the surface, especially the anomalous coarse carbides in the binder enrichment zone is the main reason for the lower strength
基金Hubei Provincial Department of Education(Q20201512)。
文摘Mo2C was prepared by microwave plasma chemical vapor deposition(MPCVD)technique with the power of 800 W and pressure of 18 kPa.Compared with traditional preparation methods,MPCVD has faster growth rate and higher purity of the products.The influence of growth time on the morphology and structure of Mo_(2)C was characterized by X-ray diffraction and Scanning Electron Microscopy.The photocatalytic performance of Mo_(2)C was tested.It was found that Mo_(2)C had good photocatalytic performance and the 6 h sample had the highest photodegradation rate,indicating the great potential of Mo_(2)C as photocatalyst.
基金funded by National Natural Science Foundation of China(51301038,51371050)Industry-Academia-Research Program of Jiangsu Province of China(BY2014127-03)+2 种基金Natural Science Foundation of Jiangsu Province of China(BK20141306)Key Research Program of Jiangsu Province of China(BE2016154)Jiangsu Province Key Laboratory of High-end Structural Materials of China(hsm1404)
文摘The morphology,microstructure and decomposition behavior of M2C carbides in high speed steels with different chemical compositions have been investigated by scanning electron microscopy,transmission electron microscopy,electron backscatter diffraction and X-ray diffraction.The results show that the morphology and substructure of M2C carbides are very sensitive to chemical compositions of high speed steels.M2C carbides present the plate-like shape in tungsten-molybdenum steel and present the polycrystal orientation in the eutectic cell.In contrast,they show the fibrous shape in molybdenum-base steel and exhibit the monocrystal orientation.Plate-like and fibrous M2C carbides are both metastable and decompose into M6 C together with MC at high temperatures.MC nucleates inside the plate-like M2C while it is formed at the fibrous M2C/matrix interface during the decomposition process.Such differences are expected to arise from different compositions of plate-like and fibrous M2C carbides.
基金the National Natural Science Foundation of China(51775540)Zhejiang Provincial Natural Science Foundation of China(LR21E050001)the Youth Innovation Promotion Association,CAS(2017338).
文摘Novel two-dimensional(2D)Nb_(2)C nanosheets were successfully prepared through a simple lultrasonic and magnetic stirring treatment from the original accordion-like powder.To further study their water-lubrication properties and deal with common oxidation problems,Nb_(2)C nanosheets with different oxidation degrees were prepared and achieved long-term stability in deionized water.Scanning electron microscope(SEM),transmission electron microscope(TEM),scanning probe microscope(SPM),X-ray powder diffraction(XRD),Raman,and X-ray photoelectron spectrometer(XPS)experiments were utilized to characterize the structure,morphology,and dispersion of Nb_(2)C nanosheets with different degrees of oxidation.The tribological behaviors of Nb_(2)C with different degrees of oxidation as additives for water lubrication were characterized using a UMT-3 friction testing machine.The wear scars formed on the 316 steel surface were measured using three-dimensional(3D)laser scanning confocal microscopy.The tribological results showed that a moderately oxidized Nb_(2)C nanosheet,which owned the composition of Nb_(2)C/Nb_(2)O5/C,displayed excellent tribological performance,with the friction coefficient(COF)decreasing by 90.3%and a decrease in the wear rate by 73.1%compared with pure water.Combining the TEM and Raman spectra,it was shown that Nb_(2)O5 nanoparticles filled in the worn zone,and the layered Nb_(2)C and C were adsorbed into the surface of the friction pair to form a protective lubricating film.This combined action resulted in an excellent lubricating performance.
基金supported by the Natural Science Foundation of China (Grant No. 52073075)Shenzhen Science and Technology Program (Grant No. KQTD20170809110344233)Science and Technology Innovation Talents Program of Henan Province (Grant No. 174200510010)。
文摘Nb_(2)S_(2)C is a van der Waals type layered superconductor with a transition temperature Tc=7.6 K.In this paper,detailed calculations of the electronic structure and topological properties of Nb_(2)S_(2)C were performed from first principles.We find that Nb2S2C is a highly anisotropic metal with multi-band characteristics.In the absence of spin-orbit coupling(SOC),there appears one pair of triply degenerate points created by band inversion along the Γ-A line.When SOC is considered,the triple points are gapped.Intriguingly,two distinct types of topological states,including topological Dirac semimetal and topological insulator states,co-emergence in the vicinity of Fermi level.Moreover,the topology of Nb_(2)S_(2)C is robust to external pressure and the Fermi level can be shifted downward to the topological Dirac semimetal state and topological insulator state at 10 GPa and 14 GPa,respectively.The results herein provide a new platform not only for the studies of physics of low-dimensional superconductor but also for further investigations of topological superconductivity.
基金supported by Natural Science Foundation of Hebei Province of China(Nos.B2021202028,B2020202052,B2019202277)Outstanding Youth Project of Guangdong Natural Science Foundation(No.2021B1515020051)+9 种基金State Key Laboratory of Reliability and Intelligence of Electrical Equipment(No.EERI_PI2020007)Hebei University of Technology,Chinathe Program for the Outstanding Young Talents of Hebei Province,China(YG.Z.)Chunhui Project of Ministry of Education of the People’s Republic of China(No.Z2017010)Department of Science and Technology of Guangdong Province(Nos.2020B0909030004,2019JC01L203)Guangdong Innovative and Entrepreneurial Team Program(No.2016ZT06C517)Science and Technology Program of Guangzhou(No.2019050001)Science and Technology Program of Zhaoqing(No.2019K038)project AP09259764“Engineering of Multifunctional Materials of Next Generation Batteries”from the Ministry of Education and Science of Kazakhstana research project FDCRP No.110119FD4504“Development of 3D solid state thin film materials for durable and safe Li-ion microbatteries”from Nazarbayev University。
文摘Extensive research has been devoted to lithium-sulfur(Li-S)batteries due to their overwhelming promises and advantages such as high theoretical capacity(1675 m Ah g^(-1)),extremely cost effectiveness and abundance and availability of sulfur.Nevertheless,a sluggish electrochemical kinetics of the battery limited by a slow conversion of lithium polysulfide(LiPSs)intermediates and Li PSs shuttle effect severely hinder its development towards industrial application.Herein,we designed the oxidized Nb2_(C)MXene with amorphous carbon(Nb_(2)O_(5)/C)composites as sulfur host using CO_(2)treatment to address the above issues.The Nb_(2)O_(5)/C composites with high conductivity are directly employed as sulfur hosts for Li-S battery capable to remarkably mitigate the shuttle phenomenon due to a combined effect of their Li PSs trapping ability and catalytic activity towards their accelerated conversion.Meanwhile,the unique layered structure of the composite facilitates ion transfer and accommodates the volume changes of the cathode during cycling.With this rational design,the resultant Li-S batteries exhibit superior electrochemical performance with a high initial specific capacity of 745 m Ah g^(-1)at 1.0 C and a reversible capacity of 620 m Ah g^(-1)at a high rate cycling at 3.0 C.
